Field of the Invention
The present invention relates to an engine system for controlling flow of exhaust gas. More particularly, the present invention relates to an engine system for controlling flow of exhaust gas capable of stably maintaining a cleaning rate of exhaust gas by stably maintaining a temperature of a diesel oxidation catalyst (DOC) or a diesel particulate filter (DPF) in an overrun condition of an engine.
Description of Related Art
In recent years, in order to respond to limitations on exhaust gas in a passenger diesel engine, a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), a nitrogen oxide cleaning unit (LNT, lean NOx trap), a selective catalytic reduction (SCR) unit, and the like have been considered.
A post processing system such as the DOC, the LNT, and the SCR mounted for the purpose of reducing exhaust gas requires a basic temperature for chemical reaction.
In general, exhaust temperature is low in an engine cool state (coolant temperature of 90° C. or less). In this region, exhaust gas is excessively exhausted after the post processing device is activated.
Accordingly, cool exhaust gas reduction has been performed by applying an exhaust temperature increasing strategy through fuel consumption sacrifice in a cool region.
However, the exhaust temperature increase is possible through combustion strategy. However, in a case of overrun (coasting run, non-combustion state), intake air is discharged to an engine exhaust port without a combustion process which cools the post-processing system so that the temperature of the post-processing system is reduced and an activation temperature reach time may be delayed.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.